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            <h2 class="title" style="clear: both"><a id="recovery-intro"></a>Recoverability</h2>
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      <p>
            An important part of DB's transactional guarantees is durability.
            <span class="emphasis"><em>Durability</em></span> means that once a
            transaction has been committed, the database modifications performed
            under its protection will not be lost due to system failure.
        </p>
      <p>
            In order to provide the transactional durability guarantee, 
            DB uses a write-ahead logging system. Every operation performed on
            your databases is described in a log before it is performed on
            your databases. This is done in order to ensure that an operation can be
            recovered in the event of an untimely application 
            or system failure. 
        </p>
      <p>
            <span>
            Beyond logging, another important aspect of durability is
            recoverability. That is,  backup and restore. </span> 
            
            DB supports a normal recovery that runs against a subset of
            your log files. This is a routine procedure used whenever your
            environment is first opened upon application startup, and it is intended to
            ensure that your database is in a consistent state.  DB also
            supports archival backup and recovery in the case of
            catastrophic failure, such as the loss of a physical disk
            drive.
        </p>
      <p>
            This book describes several different backup procedures
            you can use to protect your on-disk data. These procedures
            range from simple offline backup strategies to hot failovers. Hot failovers
            provide not only a backup mechanism, but
            also a way to recover from a fatal hardware failure.
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      <p>
            This book also describes the recovery procedures you should use
            for each of the backup strategies that you might employ.
        </p>
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            For a detailed description of backup and restore procedures, see
            <span> 
                <a class="xref" href="filemanagement.html" title="Chapter 5. Managing DB Files">Managing DB Files</a>.
            </span>
            

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